This weeks blog post is about the slurry process of GFRC concrete . Here at Modern Concrete our mission is to create beautiful hand crafted pieces that will stand up to the test of time. Slurry is just one part of that process but it's extremely important. Slurry is a multi step process vital to the surfaces final finish. The slurry is comprised of Portland cement, water, polymer & colored pigment if needed. These ingredients are mixed together to either a paste like consistency for larger pinholes or a creamery liquid mix for small pinholes. Pinholes are small voids exposed in the first wet polish of the newly demolded concrete. These pinholes are filled to ensure a super smooth finished surface on the final product.
We begin by misting the concrete with a light spray of water. This helps prevent the concrete from absorbing the moisture from the slurry mix. Slurry is then hand applied is small quarter size amounts by rubbing it onto the concrete surface. It is worked in from all directions using pressure to push the mix into any pinholes. We apply the slurry to small sections of the concrete surface (approximately 6″x6″) at a time to ensure good coverage until the entire piece is covered. A light is also used to help bring out any "hidden" pinholes that may not be seen in normal shop lighting. Covering the entire piece with the slurry allows for an even application of color. If we only spot slurried the pinholes you would see blotches after we were done that would be very dark and give the concrete the appearance of having stains.
Once the slurry has cured overnight we then wet polish the concrete surface again using diamond pads. This process is then repeated an additional two or three times until the concrete maintains a smooth pinhole free surface. The entire slurry process takes between 4-5 days. The concrete is then allowed to cure (dry out) for another 1-2 days before the sealer can be applied. We allow the concrete to fully dry out before we apply the sealer to ensure the concrete is maturing and the internal moisture has been reduced to very low levels. Dry concrete allows the sealer to penetrate into the concrete, whereas damp, wet, fresh or barely dry concrete will not. Curing (drying) of the concrete also plays an important role in the development of the strength and durability of the concrete. But that's for another post !